Clinical Interpretation of Arterial Blood Gas and Oxygenation - PDF

Clinical Interpretation of Arterial Blood Gas and Oxygenation Pio T. Esguerra II, MD, FPCP, FPCCP, DIH Associate Professor of Medicine Dean, FEU-NRMF School of Respiratory Therapy Head, Pulmonary Care, FEU-NRMF Medical Center  Anatomy  Upper respiratory tract  Lower respiratory tract t...

Clinical Interpretation of Arterial Blood Gas and Oxygenation Pio T. Esguerra II, MD, FPCP, FPCCP, DIH Associate Professor of Medicine Dean, FEU-NRMF School of Respiratory Therapy Head, Pulmonary Care, FEU-NRMF Medical Center  Anatomy  Upper respiratory tract  Lower respiratory tract trachea bronchi bronchioles alveoli Anatomy of Respiratory Tract (Broncho-pulmonary segments)  Right lung  Left lung  Upper lobe  Upper  Apical  Apico-posterior  Posterior  Anterior  Anterior  Middle lobe  Superior lingula  Lateral  Inferior lingula  Medial  Lower  Lower lobe  Superior  Superior  Antero-medial  Medial  Lateral  Anterior  Lateral  Posterior  Posterior  Chest Wall Ventilatory Organs (Thoracic Pump) Gas Exchange Organs Clinical manifestation of respiratory diseases  Dyspnea  Cough  Chest pain  hemoptysis Laboratory tests:  Sputum analysis  Culture & sensitivity  Arterial Blood Gas (ABG)  Sputum cytology Oxygen-hemoglobin dissociation curve  proportion of hemoglobin in its saturated form on the vertical axis against the prevailing oxygen tension on the horizontal axis.  important tool for understanding how our blood carries and releases oxygen.  relates oxygen saturation (sO2) and partial pressure of oxygen in the blood (pO2)  determined by what is called "Hemoglobin affinity for oxygen" (acquires and releases oxygen molecules into the fluid). 88 Oxyhemoglobin dissociation curve 9 Haldane vs Bohr  Haldane effect- describes how oxygen concentrations determine hemoglobin’s affinity to carbon dioxide.  Bohr effect- describes how CO2 and H+ concentrations affect hemoglobin’s affinity to oxygen 10 1 0 110 1 Arterial Blood Gas (ABG)  Specimen:  Arterial blood  “arterialized” capillary blood  Materials:  cotton balls (wet), rubber stopper  syringe  heparin ( 0.5ml of 1000-U/ml per 5ml blood)  ice for transport Factors affecting levels of Arterial Blood Gases  Exposure to ambient atmosphere (or air bubble)  Temperature (gas pressures & pH)  Excess heparin (lower pCO2 by 12-25%)  Transport on ice  Stable for 30 minutes Take note:  Measure ABG at 37C  For each degree (C) increase in temp.  pO2 falls by 7%  pCO2 rise by 3% 1. Careful history & physical examination 2. Electrolytes & arterial blood gas (ABG) 3. Evaluate the anion gap Anion gap= Na-(Cl+HCO3) Normal value= 10-12 meq/L Reference values: Blood Gases & Electrolytes  Arterial  Venous  pH: 7.35-7.45 mmHg  Na: 135-148 mEq/liter  K: 3.5-5.3  pCO2: 35-45  Cl: 98-106  pO2: 80-100  Anion gap: 12-18  O2 sat: 95% of pO2  Serum osmolality:  HCO3: 22-26 285-310 mOsm/kg H20 SUMMARY ALGORITHM FOR ACID-BASE INTERPRETATION pH < 7.35 7.35 – 7.45 > 7.45 ACIDOSIS NORMAL ALKALOSIS or COMPENSATED Uncompensated Uncompensated 35 - 45 PaCO2 PaCO2 35 - 45 Metabolic Acidosis pH Metabolic Alkalosis < 35 > 45 Partly Compensated < 7.4 > 7.4 Partly Compensated Metabolic Acidosis > 45 < 35 Metabolic Alkalosis Normal or Normal or Compensated Compensated Respiratory Acidosis Alkalosis Respiratory Compensated PaCO2 Compensated 22 - 26 HCO3 HCO3 22 - 26 Metabolic Respiratory Acidosis < 35 Alkalosis > 26 < 22 > 26 < 22 Uncompensated Compensated Compensated Uncompensated > 45 Respiratory Acidosis Respiratory Metabolic Respiratory Alkalosis Acidosis Alkalosis Partly Compensated Combined 35 - 45 Combined Partly Compensated Respiratory Acidosis Respiratory Respiratory Respiratory Alkalosis and Metabolic and Metabolic Acidosis Normal Acid-Base Alkalosis ABG INTERPRETATION  Check pH : Normal or Abnormal?  If abnormal, is it acidemia or alkalemia?  Check for PaCO2, is it respiratory or metabolic?  Check for compensation (same direction)  Check for combined acid-base abnormality (opposite direction)  Check for oxygenation (room air; supplementation)) HENDERSON-HASSELBACH Base pH = pk + log ------------ Acid  HCO3 (Met. 22-26) pH = (6.1) + log ---------------- (7.35-7.45) PaCO2 (Resp. 35-45) HCO3 pH = ----- PaCO2  HCO3 HCO3 pH = ------ pH = ------ PaCO2 PaCO2 Metabolic Acidosis Respiratory Acidosis HCO3 HCO3 pH = ------ pH = ------ PaCO2 PaCO2 Metabolic Alkalosis Respiratory Alkalosis  HCO3 HCO3 pH = ------ pH = ------ PaCO2 PaCO2 Uncompensated Partly Compensated Respiratory Acidosis Respiratory acidosis HCO3 N pH = ------ PaCO2 Compensated Respiratory Acidosis  HCO3 Combined pH = ------ Respiratory & Metabolic PaCO2 Alkalosis HCO3 Combined pH = ------ Respiratory & Metabolic PaCO2 Acidosis ACID-BASE BALANCE ABNORMALITY COMPENSATION RESPIRATORY ACIDOSIS ↑CO2 ↑HCO3 ALKALOSIS ↓CO2 ↓HCO3 METABOLIC ACIDOSIS ↓HCO3 ↓CO2 ALKALOSIS ↑HCO3 ↑CO2  26 year old female, complaining of dyspnea and chest pain, RR– 30/min  pH 7.49  pCO2 30  pO2 98  HCO3 24  Sat 99% Uncompensated Respiratory Alkalosis OXYGENATION AT ROOM AIR  Patients < 60 y/o Expected pO2 = 80 –100 mm Hg  Patients > 60 Expected pO2 = 80 – ( years above 60) Ex. 70 year-old male Expected pO2 = 80 – 10 = 70 OXYGENATION STATUS  Patients < 60 y/o pO2 < 80 = Hypoxemic 80 –100 = Normal > 100 = more than adequate  Patients > 60 y/o pO2 < Expected = hypoxemic pO2 = expected = Normal pO2 > 100 = more than adequate Interpretation: OXYGENATION STATUS (ABG TAKEN AT ROOM AIR)  Normal  Hypoxemia  Mild- 60-79  Moderate- 40-59  Severe- 60 years old 400 – ( age above 60 x 5) Ex. 75 yrs old 400 – ( 15 x 5) = 325 DESIRED FiO2 d PaO2 PaCO2 -------- + ------- aAO2 0.8 DESIRED FiO2 = ----------------------- 713 ALVEOLAR-ARTERIAL O2 DIFFERENCE (A-aDO2) ALVEOLAR PO2 = 713(FiO2) – PaCO2/0.8 A-aDo2 = ALVEOLAR PO2 – arterial PO2 NORMAL = < 15 @ 30 y/o and add 3 for every decade above 30  Arterial PO2 (ABG) Aao2 ratio = ------------------------ Alveolar PO2 ( 713 x FiO2 – Pa CO2/0.8) NORMAL = 0.75 CAUSES OF HYPOXEMIA  HYPOVENTILATION  DECREASED FiO2  V/Q MISMATCH  SHUNT  DIFFUSION ABNORMALITIES Diagnostic approach to patient with hypoxemia 541 2 Acid-Base Disturbances  Metabolic Alkalosis  Exogenous steroids  GI loss (vomitting, etc.)  Renal loss (Conn syndrome, Cushing)  Decreased chloride intake  Diuretics  Bicarbonate administration  Contraction alkalosis Acid-Base Disturbances  Respiratory Alkalosis  Hyperventilation of any cause  Anemia  Pulmonary embolism  Sarcoid  Anxiety  Pain Acid-Base Disturbances  Metabolic Acidosis  Anion gap=(Na+K)-(HCO3+Cl)  NV= 8-14  Nonanion gap  Diarrhea  Renal tubular acidosis (RTA)  Increased Anion gap  Lactate (sepsis, ischemia)  Aspirin,Methanol  Uremia, DKA  INH Acid-Base Disturbances  Respiratory Acidosis  Hypoventilation  COPD  Pickwickian syndrome  Obesity  Suffocation  Opiate overdose  Sleep apnea